In order to presume an unidentified component contained in a sample (hereinafter referred to as “unidentified component”), scan measurement is widely used, which uses a chromatograph mass spectrometer structured by combining a chromatograph, such as a gas chromatograph (GC) and a liquid chromatograph (LC), with a mass spectrometer (MS). A combined apparatus (LC/MS) of the LC with a mass spectrometer having one mass separation unit is used to perform MS scan measurement, whereas a combined apparatus (LC/MS/MS) of the LC with a mass spectrometer having a collision cell and mass separation units, which are positioned before and after the collision cell, is used to perform MS/MS scan measurement.
In LC/MS scan measurement, ions generated from unidentified components are measured as they are to acquire the mass spectra of the ions. In product ion scan measurement using the LC/MS/MS, ions are generated from unidentified compounds separated in time in a column of the LC. Out of the generated ions, ions having a specific mass-to-charge ratio are selected as a precursor ion in a front-stage mass separation unit, and then the precursor ion is fragmented in the collision cell to generate product ions. The generated product ions are further subjected to scan measurement in a rear-side mass separation unit to acquire the mass spectra of the product ions. Hence, it is possible to obtain more detailed information about the molecular structure of the unidentified component than that in the LC/MS scan measurement. Therefore, the product ion scan measurement with the LC/MS/MS is typically performed in presuming a compound having a complicated molecular structure, such as agricultural chemicals and medicinal substances (see, for example, Patent Literature 1).
When product ion scan measurement is performed with use of the LC/MS/MS to inspect whether the sample contains agricultural chemicals, medicinal substance, or the like, a plurality of compounds, whose mass spectra of product ions are known, are selected as inspection subjects in advance. Then, measurement conditions for each of the plurality of subject compounds are set. The conditions include values of the mass-to-charge ratios of precursor ions that characterize each of the subject compounds. While an unidentified component is being eluted from a column of the LC, product ion scan measurements are executed in sequence under the plurality of measurement conditions to acquire the mass spectra of the subject compounds. When an unidentified component corresponds to one of the subject compounds, a mass spectrum (i.e., the position (mass-to-charge ratio) and the intensity of mass peaks on the mass spectrum) obtained under the measurement condition corresponding to the corresponding subject compound, matches with the mass spectrum representing (the position and the intensity of mass peaks of) the corresponding subject compound. Therefore, it is possible to determine whether or not the unidentified component is one of the subject compounds by confirming matching between the positions and the intensities of mass peaks on the mass spectra, each acquired by measurement performed under the plurality of measurement conditions during elution of the unidentified component, and the positions and the intensities of the mass peaks on the mass spectra of the subject compounds.
In recent years, a database storing the mass spectra of the product ions concerning a large number of compounds is provided. If a matching degree between the positions (mass-to-charge ratios) and the intensities of the mass peaks on the mass spectra of various compounds in the database and the positions and the intensities of the mass peaks on the mass spectra acquired by measurement is calculated by a data processor, an analyst can confirm the result to presume an unidentified component contained in a sample in a relatively simple manner.
However, in the inspection of prohibited substances contained in a sample derived from a living body, for example, not only principal subject compounds (hereinafter referred to as “basic compounds”) but also compounds (similar compounds) whose molecular structures are partially altered from those of the basic compounds need to be detected. A series of subject compound groups, including the basic compounds and the compounds similar to the basic compounds, have molecular structures mostly in common. However, since the molecular structures of the similar compounds are partially altered, the mass spectra of their product ions do not match with the mass spectra of the product ions of the basic compounds. Accordingly, the analyst cannot determine the presence of the similar compounds simply by confirming the result of calculating the matching degree with the mass spectra stored in the compound database. Therefore, in the inspection of medicinal substances and the like, the analyst confirms the presence of similar substances by displaying on a display device a plurality of mass spectra acquired by performing MS/MS measurement and comparing the positions and the intensities of mass peaks on each of the mass spectra to find out mass peaks that characterize the subject compound groups.